Fluorine-free fused ring heteroaromatic photoacid generators and resist compositions containing the same

ABSTRACT

The present invention relates to a fluorine-free photoacid generator (PAG) and a photoresist composition containing the same. The PAG is characterized by the presence of an onium cationic component and a fluorine-free fused ring heteroaromatic sulfonate anionic component containing one or more electron withdrawing substituents. The onium cationic component of the PAG is preferably a sulfonium or an iodonium cation. The photoresist composition further contains an acid sensitive imaging polymer. The photoresist composition is especially useful for forming material patterns on a semiconductor substrate using 193 nm (ArF) lithography.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims priority toco-pending U.S. patent application Ser. No. 12/692,961, filed Jan. 25,2010, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to photolithography, and more particularly tofused ring heteroaromatic photoacid generators which are fluorine-freeand efficiently generate acids upon exposure to UV light. This inventionis also directed to resist compositions containing the inventivefluorine-free fused ring heteroaromatic photoacid generators and methodsof using the resist compositions in photolithography.

BACKGROUND OF THE INVENTION

Miniaturized electronic components such as integrated circuits aretypically manufactured using photolithography technology. In aphotolithography process, a photoresist layer is formed on a substrate,such as a silicon wafer. The substrate is baked to remove any solventremained in the photoresist layer. The photoresist is then exposedthrough a photomask with a desired pattern to a source of actinicradiation. The radiation exposure causes a chemical reaction in theexposed areas of the photoresist and creates a latent imagecorresponding to the mask pattern in the photoresist layer. Thephotoresist is next developed in a developer solution, usually anaqueous base solution, to remove either the exposed portions of thephotoresist for a positive photoresist or the unexposed portions of thephotoresist for a negative photoresist. The patterned photoresist canthen be used as a mask for subsequent fabrication processes on thesubstrate, such as deposition, etching, or ion implantation processes.

One type of photoresist employed in the prior art is a chemicallyamplified photoresist which uses acid catalysis. Chemically amplifiedphotoresists have increased sensitivity to exposure energy overnon-chemically amplified photoresists. A chemically amplifiedphotoresist is especially useful when relatively short wavelengthradiation is employed, such as deep UV radiation (150-315 nmwavelengths) and mid-UV radiation (350-450 nm wavelengths).

A typical prior art chemically amplified photoresist, for example, isformulated by dissolving an acid sensitive base polymer and a photoacidgenerator (PAG) in a casting solution. The base polymer in a chemicallyamplified positive photoresist typically has acid labile groups bondedto the polymer backbone. When such a photoresist is exposed toradiation, the PAG absorbs photons and produces an acid. The photogenerated acid then causes catalytic cleavage of the acid labile groups.A single acid molecule generated in this manner may be capable ofcleaving multiple acid labile groups on the base polymer. Thus, fewerphotons are needed to render the exposed portion of the photoresistsoluble in the developer solution.

Because of the relatively low intensity of a 193 nm laser source andrelatively high binding energy of acid labile groups in a 193 nmphotoresist, PAGs which can produce stronger Bronsted acid with highsensitivity are preferred to realize such a chemical amplification incommercial 193 nm photolithography. Fluorine-containing PAGs, such asperfluorooctyl sulfonate (PFOS) and perfluoroalkyl sulfonate (PFAS), aregenerally preferred PAGs in 193 nm photoresist system partially becausethey result in generation of strong acids.

In recent years, however, there has been a desire in themicroelectronics industry to eliminate the use of perfluorinated carbons(PFCs) including PFOS and PFAS due to their detrimental effects onenvironment, human and animals. Thus, there is a desire to findalternative PAGs which can be used without adversely impacting theperformance of lithographic processes. There has also been a desire tominimize or eliminate fluorine content in photoresist in order toimprove etch resistance and to improve process latitude in high numericaperture (NA>0.95) imaging processes. Accordingly, there is a need fornew and improved fluorine-free PAGs and chemically amplified photoresistcompositions that enable the substantial reduction or avoidance offluorine content in photoresist compositions.

SUMMARY OF THE INVENTION

The present invention provides fluorine-free photoacid generators whichare a viable alternative to the PFC-containing photoacid generatorscurrently used in the industry. This invention also provides photoresistcompositions containing such a fluorine-free photoacid generator thatshow excellent optical clarity and thermal stability and havelithographic performance equal to or better than that of photoresistshaving the PFC-containing photoacid generators.

In one aspect, the present invention relates to a fluorine-freephotoacid generator including an onium cationic component and an anioniccomponent having one of the following two structures:

wherein:

X is selected from the group consisting of S, O and NR;

R is selected from the group consisting of H; linear, branched,tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;unsubstituted and substituted aromatic groups; and unsubstituted andsubstituted heteroaromatic groups;

Y is selected from the group consisting of C and N; and

each of G₁-G₅ is selected from the group consisting of R and an electronwithdrawing moiety, provided that when Y is N, G₁ is not present in thestructure and at least one of G₁-G₅ is an electron withdrawing moiety.

The onium cationic component of the fluorine-free photoacid generator ispreferably selected from the group consisting of sulfonium cations andiodonium cations. The onium cationic component preferably includes anaromatic moiety.

In another aspect, the present invention relates to a photoresistcomposition including:

-   -   (a) an acid sensitive imaging polymer; and    -   (b) a fluorine-free photoacid generator comprising an onium        cationic component and an anionic component having one of the        following two structures:

-   -   -   wherein:        -   X is selected from the group consisting of S, O and NR;        -   R is selected from the group consisting of H; linear,            branched, tertiary, or cyclic alkyl; linear, branched,            tertiary or cyclic alkoxyl; unsubstituted and substituted            aromatic groups; and unsubstituted and substituted            heteroaromatic groups;        -   Y is selected from the group consisting of C and N; and        -   each of G₁-G₅ is selected from the group consisting of R and            an electron withdrawing moiety, provided that when Y is N,            G₁ is not present in the structure and at least one of G₁-G₅            is an electron withdrawing moiety.

The imaging polymer of the photoresist composition preferably has alactone moiety. The imaging polymer preferably has a weightconcentration ranging from about 1% to about 30% of the total weight ofthe photoresist composition. The fluorine-free photoacid generatorpreferably has a weight concentration ranging from about 0.5% to about20% based on the total weight of said imaging polymer.

In still another aspect, the present invention relates to a method offorming a patterned material feature on a substrate including the stepsof:

-   -   (a) providing a material layer on a substrate;    -   (b) forming a photoresist layer over the material layer, the        photoresist comprising:        -   (i) an acid sensitive imaging polymer; and        -   (ii) a fluorine-free photoacid generator comprising an onium            cationic component and an anionic component one of the            following two structures:

-   -   -   wherein:        -   X is selected from the group consisting of S, O and NR;        -   R is selected from the group consisting of H; linear,            branched, tertiary, or cyclic alkyl; linear, branched,            tertiary or cyclic alkoxyl; unsubstituted and substituted            aromatic groups; and unsubstituted and substituted            heteroaromatic groups;        -   Y is selected from the group consisting of C and N; and        -   each of G₁-G₅ is selected from the group consisting of R and            an electron withdrawing moiety, provided that when Y is N,            G₁ is not present in the structure and at least one of G₁-G₅            is an electron withdrawing moiety;

    -   (c) patternwise exposing the photoresist layer to radiation,        thereby creating a pattern of radiation-exposed regions in the        photoresist layer;

    -   (d) selectively removing portions of the photoresist layer to        expose portions of the material layer; and

    -   (e) etching or ion implanting the exposed portions of the        material layer, thereby forming the patterned material feature.

The radiation of the method is preferably provided by an ArF laser.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It will be understood that when an element, such as a layer, is referredto as being “on” or “over” another element, it can be directly on theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly on” or “directly over”another element, there are no intervening elements present.

The present invention provides a fluorine-free photoacid generator (PAG)which is a viable alternative to the PFC-containing photoacid generatorscurrently used in the industry. The fluorine-free PAG is generallycharacterized by the presence of an onium cationic component and ananionic component having one of the following two structures:

wherein:

X is selected from the group consisting of S, O and NR;

R is selected from the group consisting of H; linear, branched,tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;unsubstituted and substituted aromatic groups; and unsubstituted andsubstituted heteroaromatic groups;

Y is selected from the group consisting of C and N; and

each of G₁-G₅ is selected from the group consisting of R and an electronwithdrawing moiety, provided that when Y is N, G₁ is not present in thestructure and at least one of G₁-G₅ is an electron withdrawing moiety.

In one embodiment of the present invention, one of G₁-G₅ is an electronwithdrawing moiety. In another embodiment of the present invention, atleast two of G₁-G₅ are electron withdrawing moieties. Examples of theelectron withdrawing moieties suitable for the present inventioninclude, but are not limited to, CN, NO, NO₂, Cl, Br, I, SO₂Me, and CHO.Preferably, at least one of G₁-G₅ is CN or NO₂.

The onium cationic component of the fluorine-free PAG is preferably asulfonium cation or an iodonium cation. Preferably, the onium cationiccomponent has an aromatic moiety. The aromatic structure of the cationiccomponent generally improves the thermal stability of the resultingfluorine-free PAG. Two preferred cationic component for the presentinvention are:

wherein each of R₁, R₂, R₃, R₄, and R₅ is independently selected fromthe group consisting of H; linear, branched, tertiary, or cyclic alkyl;linear, branched, tertiary or cyclic alkoxyl; unsubstituted andsubstituted aromatic groups; and unsubstituted and substitutedheteroaromatic groups. Examples of a sulfonium cation of the structure(III) are:

An example of an iodonium cation of the structure (IV) is:

Examples of the anionic component of structures (I) and (II) are:

The invention is not limited to any specific method for synthesizing thefluorine-free PAGs of the invention. One possible synthesis route isshown in Scheme 1 below.

As shown in Scheme 1, in one embodiment, the synthesis of thefluorine-free fused-ring heteroaromatic PAGs starts from the nitrosubstitution reaction of a fused-ring heteroaromatic sulfonyl chloride,followed by a one-pot reaction to convert the nitro-substitutedfused-ring heteroaromatic sulfonyl chloride to its corresponding silversulfonate. The nitro-substituted fused-ring heteroaromatic sulfonylchloride reacts with silver carbonate to afford the silver salt in solidphase at almost quantitative yield. The resulting silver salt thenreacts with a corresponding sulfonium (or iodonium) source to afford thedesired fluorine-free fused-ring heteroaromatic PAG. The chemicalstructures of the resulting fluorine-free fused-ring heteroaromatic PAGscan be confirmed by their NMR spectra. In the instance of synthesis ofthe triphenyl sulfonium mono nitro-benzo[b]thiophene-2-sulfonate(TPSTBNO) as shown in Scheme 1, the resulting PAG is a mixture of twoisomers A and B with a molar ratio of 65:35.

The invention also encompasses a photoresist composition containing thefluorine-free PAGs of the present invention. The photoresist compositionhas an acid sensitive imaging polymer and a fluorine-free PAG having anonium cationic component and an anionic component having one of thefollowing two structures:

wherein:

X is selected from the group consisting of S, O and NR;

R is selected from the group consisting of H; linear, branched,tertiary, or cyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;unsubstituted and substituted aromatic groups; and unsubstituted andsubstituted heteroaromatic groups;

Y is selected from the group consisting of C and N; and

each of G₁-G₅ is selected from the group consisting of R and an electronwithdrawing moiety, provided that when Y is N, G₁ is not present in thestructure and at least one of G₁-G₅ is an electron withdrawing moiety.

The imaging polymer is preferably capable of undergoing chemicaltransformations upon exposure of the photoresist composition to UV lightwhereby a differential in the solubility of the polymer in either theexposed regions or the unexposed regions is created. The imaging polymermay be either a positive-tone imaging polymer or a negative-tone imagingpolymer. When the imaging polymer is a positive-tone imaging polymer, itpreferably includes acid sensitive side chains which can undergocatalytic cleavage in the presence of an acid generated by the inventivePAG. In such a polymer, the acid sensitivity exists because of thepresence of acid sensitive side chains that are bonded to the polymerbackbone. Such acid sensitive polymers including acid sensitive sidechains are conventional and are well known in the art. Preferably, theimaging polymer is one suitable for use in 193 nm (ArF) lithography.

In some embodiments, the acid sensitive side chains of the acidsensitive polymers are protected with various acid labile protectinggroups that are well known to those skilled in the art. For example, theacid sensitive side chains may be protected with high activation energyprotecting groups such as t-butyl ester or t-butyl carbonyl groups, alow activation energy protecting group such as acetal, ketal, orsilyethers, or a combination of both low and high activation energyprotecting groups may also be used.

The imaging polymer of the invention preferably contains a lactonemoiety, more preferably a pendant lactone moiety. Examples of imagingpolymers containing lactone moieties are disclosed in US PublishedPatent Application No. 20060216643A1, and U.S. Pat. Nos. 7,087,356,7,063,931, 6,902,874, 6,730,452, 6,627,391, 6,635,401 and 6,756,180.Some preferred lactone-containing monomeric units suitable for thepresent invention are:

Preferred imaging polymers contain at least about 5 mole % oflactone-containing monomeric units based on the total monomeric units inthe imaging polymer, more preferably about 10-50 mole %, most preferablyabout 15-35 mole %.

The photoresist compositions of the invention preferably contain asolvent which is capable of dissolving the acid sensitive imagingpolymer. Examples of such solvents include, but are not limited to:ethers, glycol ethers, aromatic hydrocarbons, ketones, esters and thelike. A solvent system including a mixture of the aforementionedsolvents is also contemplated herein. Suitable glycol ethers include:2-methoxyethyl ether (diglyme), ethylene glycol monomethyl ether,propylene glycol monomethyl ether, propylene glycol monomethyletheracetate (PGMEA) and the like. Suitable aromatic hydrocarbon solventsthat include: toluene, xylene, and benzene. Examples of ketones include:methylisobutylketone, 2-heptanone, cycloheptanone, and cyclohexanone. Anexample of an ether solvent is tetrahydrofuran, whereas ethyl lactateand ethoxy ethyl propionate are examples of ester solvents that may beemployed herein.

In addition to the above components, the photoresist composition mayalso include other components such as photosensitizers, bases,surfactants or other additives. If desired, combinations or mixtures ofthese other components may be used (e.g., a photosensitizer and a base).

The optional photosensitizer is preferably one containing chromophoresthat are capable of absorbing irradiation in 193 nm (ArF) lithography.Illustrative examples of such compounds include, but are not limited to:9-anthracene methanol, coumarins, 9,10-bis(trimethoxysilyethynyl)anthracene and polymers containing these chromophores.

The optional bases that can be employed in the present inventioninclude, but are not limited to: aliphatic amines, aromatic amines,carboxylates, hydroxides, or combinations thereof and the like.

The optional surfactants that can be employed in the photoresistcompositions include any surfactant that is capable of improving thecoating homogeneity of the chemically amplified photoresist compositionof the present invention. Illustrative examples include:fluorine-containing surfactants such as 3M's FC-430® andsiloxane-containing surfactants such as Union Carbide's Silwet® series.

The photoresist compositions of the invention preferably comprise fromabout 1 to about 30 weight % imaging polymer, from about 50 to about 95weight % solvent, and from about 0.1 to about 20 weight % fluorine-freePAG (the weight % of the fluorine-free PAG is based on the total weightof imaging polymer present in the composition).

When a photosensitizer is employed, it is preferably present in anamount of from about 0.001 to about 8 weight %, based on the totalweight of imaging polymer. If a base is employed, the optional base ispreferably present in an amount of from about 0.1 to about 5 weight %,based on the total weight of imaging polymer. When a surfactant isemployed, it is preferably present in amount of from about 0.001 toabout 0.1 weight %, based on the total weight of imaging polymer.

More preferably, the photoresist composition comprises from about 5 toabout 20 weight % of imaging polymer, from about 80 to about 95 weight %solvent, and from about 0.5 to about 15 weight % of fluorine-freephotoacid generator (based on the total weight of imaging polymerpresent in the composition), optionally, from about 0.01 to about 5weight % photosensitizer, based on the total weight of imaging polymer,optionally, from about 0.1 to about 3 weight % base, based on the totalweight of imaging polymer, and optionally, from about 0.001 to about0.01 weight % surfactant, based on the total weight of imaging polymer.

Note that the amounts given above are exemplary and that other amountsof each of the above components, which are typically employed in thephotolithography industry, can also be employed herein.

The present invention also encompasses a method of using the photoresistcompositions of the invention to form patterned material features on asubstrate. Such a method includes:

-   -   (a) providing a material layer on a substrate;    -   (b) forming a photoresist layer over the material layer, the        photoresist comprising:        -   (i) an acid sensitive imaging polymer; and        -   (ii) a fluorine-free photoacid generator comprising an onium            cationic component and an anionic component one of the            following two structures:

-   -   -   wherein:        -   X is selected from the group consisting of S, O and NR;        -   R is selected from the group consisting of H; linear,            branched, tertiary, or cyclic alkyl; linear, branched,            tertiary or cyclic alkoxyl; unsubstituted and substituted            aromatic groups; and unsubstituted and substituted            heteroaromatic groups;        -   Y is selected from the group consisting of C and N; and        -   each of G₁-G₅ is selected from the group consisting of R and            an electron withdrawing moiety, provided that when Y is N,            G₁ is not present in the structure and at least one of G₁-G₅            is an electron withdrawing moiety;

    -   (c) patternwise exposing the photoresist layer to radiation,        thereby creating a pattern of radiation-exposed regions in the        photoresist layer;

    -   (d) selectively removing portions of the photoresist layer to        expose portions of the material layer; and

    -   (e) etching or ion implanting the exposed portions of the        material layer, thereby forming the patterned material feature.

The substrate in the present invention is suitably any substrateconventionally used in processes involving photoresists. For example,the substrate can be silicon, silicon oxide, aluminum-aluminum oxide,gallium arsenide, ceramic, quartz, copper or any combination thereof,including multilayers. The substrate can include one or moresemiconductor layers or structures and can include active or operableportions of semiconductor devices.

The material layer may be a metal conductor layer, a ceramic insulatorlayer, a semiconductor layer or other material depending on the stage ofthe manufacture process and the desired material set for the endproduct. The photoresist compositions of the invention are especiallyuseful for lithographic processes used in the manufacture of integratedcircuits on semiconductor substrates. The photoresist compositions ofthe invention can be used in lithographic processes to create patternedmaterial layer structures such as metal wiring lines, holes for contactsor vias, insulation sections (e.g., damascene trenches or shallow trenchisolation), trenches for capacitor structures, ion implantedsemiconductor structures for transistors, etc. as might be used inintegrated circuit devices.

In some cases, a bottom antireflective coating and/or underlayer coating(e.g., a planarizing underlayer) may be applied between the photoresistlayer and the material layer. In other cases, a top antireflectivecoating layer may be applied over the photoresist layer. The inventionis not limited to the use of antireflective reflective coatings and/orunderlayer materials, nor specific compositions of those coatings ormaterials.

The photoresist layer may be formed by virtually any standard meansincluding spin coating. The photoresist layer may be baked (postapplying bake (PAB)) to remove any solvent from the photoresist andimprove the coherence of the photoresist layer. The preferred range ofthe PAB temperature for the photoresist layer is from about 70° C. toabout 150° C., more preferably from about 90° C. to about 130° C. Thepreferred range of thickness of the first layer is from about 20 nm toabout 400 nm, more preferably from about 50 nm to about 300 nm.

The photoresist layer is then patternwise exposed to the desiredradiation. The radiation employed in the present invention can bevisible light, ultraviolet (UV), extreme ultraviolet (EUV) and electronbeam (E-beam). It is preferred that the imaging wavelength of theradiation is about 248 nm, 193 nm or 13 nm. It is more preferred thatthe imaging wavelength of the radiation is about 193 nm (ArF laser). Thepatternwise exposure is conducted through a mask which is placed overthe photoresist layer.

After the desired patternwise exposure, the photoresist layer istypically baked (post exposure bake (PEB)) to further complete theacid-catalyzed reaction and to enhance the contrast of the exposedpattern. The preferred range of the PEB temperature is from about 70° C.to about 120° C., more preferably from about 90° C. to about 110° C. Insome instances, it is possible to avoid the PEB step since for certainchemistries, such as acetal and ketal chemistries, deprotection of theresist polymer proceeds at room temperature. The post-exposure bake ispreferably conducted for about 30 seconds to 5 minutes.

After PEB, if any, the photoresist structure with the desired pattern isobtained (developed) by contacting the photoresist layer with an aqueousalkaline solution which selectively dissolves the areas of thephotoresist which were exposed to radiation in the case of a positivephotoresist (or the unexposed areas in the case of a negativephotoresist). Preferred aqueous alkaline solutions (developers) areaqueous solutions of tetramethyl ammonium hydroxide (TMAH). Theresulting lithographic structure on the substrate is then typicallydried to remove any remaining developer. If a top antireflective coatinghas been used, it is preferably also dissolved by the developer in thisstep.

The pattern from the photoresist structure may then be transferred tothe exposed portions of underlying material layer of the substrate byetching with a suitable etchant using techniques known in the art;preferably the transfer is done by reactive ion etching or by wetetching. Once the desired pattern transfer has taken place, anyremaining photoresist may be removed using conventional strippingtechniques. Alternatively, the pattern may be transferred by ionimplantation to form a pattern of ion implanted material.

Examples of general lithographic processes where the composition of theinvention may be useful are disclosed in U.S. Pat. Nos. 4,855,017;5,362,663; 5,429,710; 5,562,801; 5,618,751; 5,744,376; 5,801,094;5,821,469 and 5,948,570. Other examples of pattern transfer processesare described in Chapters 12 and 13 of “Semiconductor Lithography,Principles, Practices, and Materials” by Wayne Moreau, Plenum Press,(1988). It should be understood that the invention is not limited to anyspecific lithography technique or device structure.

The invention is further described by the examples below. The inventionis not limited to the specific details of the examples.

EXAMPLES Example 1 Synthesis of mono nitro-benzo[b]thiophene-2-sulfonylchloride

To a solution of benzo[b]thiophene-2-sulfonyl chloride (1.165 g, 5 mmol)in 25 mL of dichloromethane was added 3.6 mL of concentrated nitric acid(≧22.05 mol/L) dropwise, the resulting mixture was refluxed overnightand cooled to room temperature before it was poured into 20 gram ofcrushed ice. The organic layer was separated and the aqueous layer wasextracted by 220 mL 2 dichloromethane. The organic layers were combinedand dried over MgSO₄. Solvent was then removed by rotary evaporator. Thecrude product was purified by flash column chromatography with an eluentof hexane, followed by a gradient eluent of hexane/ethyl acetate(6/1-3/1) to afford 0.58 g of product (mixture of 65% of4-nitro-benzo[b]thiophene-2-sulfonyl chloride and 35% of7-nitro-benzo[b]thiophene-2-sulfonyl chloride).

Example 2 Synthesis of silver mono nitro-benzo[b]thiophene-2-sulfonate

To a solution of mono nitro-benzothiophene-2-sulfonate (0.5177 g, 1.86mmol) in 50 mL of acetonitrile and 1 mL of water was added silvercarbonate (0.6169 g, 2.24 mmol) in portions in darkness. The resultingsuspension was stirred overnight for 9 days, until no starting materialis shown on the thin layer chromatography with an eluent of hexane/ethylacetate (1:4). The mixture was filtered through half an inch of Celite®and the solid was washed with 3×40 mL acetonitrile. The organic filtratewas combined and organic solvent was removed via rotary evaporator todryness and thus afforded 0.668 g of viscous solid with a yield of98.2%. The resulting compound was not purified for further reactions.

Example 3 Synthesis of triphenyl sulfonium mononitro-benzo[b]thiophene-2-sulfonate

(TPSTBNO)

To a solution of silver mono nitro-benzo[b]thiophene-2-sulfonate (0.668g, 0.1.83 mmol) in 80 mL of acetonitrile and 4 mL of water was added asolution of triphenyl sulfonium bromide (0.6271 g, 1.83 mmol) in 35 mLof acetonitrile and 1 mL of water. The resulting mixture was stirredovernight for 3 days before it was filtered. The resulting solution wasfiltered though 1 inch of Celite®/aluminum oxide basic/Celite® layer andwashed with 25 mL of acetonitrile and 25 mL of acetone. The organicsolvent was removed via rotary evaporator and the residue wasre-dissolved in 50 mL of 2-butanone, dried over magnesium sulfate overnight and filtered though 1 inch of Celite®. Solvent was removed byrotary evaporator and dried over vacuum oven to dryness and thusafforded 0.71 g of product with a yield of 70%. A melting point of 243°C. was obtained with TPSTBNO in a DSC measurement (10° C./min, nitrogen5 mL/min). No obvious decomposition up to 2500 C. was observed in theDSC measurement.

Example 4 Photoresist Formulation 1

4.9967 g of a photoresist polymer consisting of 15 mol % of2-trifluoromethanesulfonylamino methacrylate, 45 mol % of2-methyl-2-adamantyl methacrylate and 40 mol % of5-methacryloyloxy-2,6-norbornanecarbo-γ-lactone (S1) (20 wt % solutionin PGMEA), 0.2541 g of triphenyl sulfonium nonafluorobutanesulfonate(TPSPFBuS) (19.6 wt % solution in PGMEA), 0.3092 g of N-Boc-pyrolidine(1 wt % solution in PGMEA), 5.9311 g of PGMEA and 4.4975 g ofcyclohexanone were mixed and rotated overnight, filtered though 0.2 μmPTFE disc to afford formulation 1.

Example 5 Photoresist Formulation 2

5.0508 g of photoresist polymer S1 (20 wt % solution in PGMEA), 0.0467 gof TPSTBNO, 0.3057 g of N-Boc-pyrolidine (1 wt % solution in PGMEA),6.0932 g of PGMEA and 4.4515 g of cyclohexanone were mixed and rotatedovernight, filtered though 0.2 μm PTFE disc to afford formulation 2.

Example 6 Photoresist Formulation 3

3.1826 g of photoresist polymer Si (26.75 wt % solution in PGMEA),0.2190 g of TPSPFBuS (19.6 wt % solution in PGMEA), 0.2572 g ofN-Boc-pyrolidine (1 wt % solution in PGMEA), and 14.2645 g of PGMEA weremixed and rotated overnight, filtered though 0.2 μm PTFE disc to affordformulation 3.

Example 7 Photoresist Formulation 4

7.4842 g of photoresist polymer Si (26.75 wt % solution in PGMEA),0.0932 g of TPSTBNO, 1.0484 g of N-Boc-2-phenyl benzimidazole (1 wt %solution in PGMEA), 30.4721 g of PGMEA and 0.5974 g of -butyrolactonewere mixed and rotated overnight, filtered though 0.2 μm PTFE disc toafford formulation 4.

Physical Properties:

Thin solid films were prepared by spin-coating photoresist formulationsover 5 inch silicon wafers at the spin rate of 1500 rpm for 30 seconds.The resulting films were soft baked at 110° C. for 60 seconds. Thethickness, n and k were measured by VASE ellipsometry, OD values werecalculated from k.

TABLE 1 Physical properties of photoresist composite thin films for 193nm lithography. Thickness n Es Formulation PAG (nm) (193 nm) k (mJ/cm²)1 TPSPFBuS 180 1.6993 0.035 20 2 TPSTBNO 180 1.6966 0.039 35

Lithographic Evaluation:

For lithographic evaluation, the prepared photoresists formulation wasspin-coated for 30 seconds onto an antireflective coating material layerapplied on silicon wafers. In the case of 193 nm immersion lithography,a topcoat layer was applied above photoresist layer. The resist film wasbaked at 110C for 60 seconds on a hotplate for 60 seconds. The waferswere then exposed to 193 nm radiation (ASML, scanner 0.75 NA, and ASML,immersion scanner 1.35 NA, respectively). The exposure pattern was anarray of lines and spaces of various dimensions down to 50 nm. Theexposed wafer was then post-exposure baked on a hot plate at 120C for 60seconds. The wafers were puddle developed by 0.263 N TMAH developer for60 seconds. The resulting patterns of the photoresist imaging layerswere examined by scanning electron microscopy (SEM). The photospeedresults were obtained from the images of 150 nm line/150 nm space and 50nm line/50 nm space, respectively.

TABLE 2 Physical properties of photoresist composite thin films for 193nm immersion lithography. Thick- n E_(cd) Formu- ness (193 (mJ/ lationPAG (nm) nm) k cm²) MEEF LWR 3 TPSPFBuS 120 1.6997 0.035 13 3.1 12.2 4TPSTBNO 120 1.6985 0.039 28 3.23 8.4

While the present invention has been particularly shown and describedwith respect to preferred embodiments, it will be understood by thoseskilled in the art that the foregoing and other changes in forms anddetails may be made without departing from the spirit and scope of theinvention. It is therefore intended that the present invention not belimited to the exact forms and details described and illustrated butfall within the scope of the appended claims.

1. A fluorine-free photoacid generator, said photoacid generatorcomprising an onium cationic component and an anionic component havingone of the following two structures:

wherein: X is selected from the group consisting of S, O and NR; R isselected from the group consisting of H; linear, branched, tertiary, orcyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;unsubstituted and substituted aromatic groups; and unsubstituted andsubstituted heteroaromatic groups; Y is selected from the groupconsisting of C and N; and each of G₁-G₅ is selected from the groupconsisting of R and an electron withdrawing moiety, provided that when Yis N, G₁ is not present in the structure and at least one of G₁-G₅ is anelectron withdrawing moiety.
 2. The photoacid generator of claim 1wherein at least one of G₁-G₅ is an electron withdrawing moiety selectedfrom the group consisting of CN, NO, NO₂, Cl, Br, I, SO₂Me, and CHO. 3.The photoacid generator of claim 2 wherein at least one of G₁-G₅ isselected from the group consisting of CN and NO₂.
 4. The photoacidgenerator of claim 2 wherein at least two of G₁-G₅ are electronwithdrawing moieties.
 5. The photoacid generator of claim 1 wherein saidonium cationic component is selected from the group consisting ofsulfonium cations and iodonium cations.
 6. The photoacid generator ofclaim 5 wherein said onium cationic component comprises an aromaticmoiety.
 7. The photoacid generator of claim 6 wherein said oniumcationic component has a structure selected from the group consisting of

wherein each of R₁, R₂, R₃, R₄, and R₅ is independently selected fromthe group consisting of H; linear, branched, tertiary, or cyclic alkyl;linear, branched, tertiary or cyclic alkoxyl; unsubstituted andsubstituted aromatic groups; and unsubstituted and substitutedheteroaromatic groups.
 8. A photoresist composition comprising: (a) anacid sensitive imaging polymer; and (b) a fluorine-free photoacidgenerator comprising an onium cationic component and an anioniccomponent having one of the following two structures:

wherein: X is selected from the group consisting of S, O and NR; R isselected from the group consisting of H; linear, branched, tertiary, orcyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;unsubstituted and substituted aromatic groups; and unsubstituted andsubstituted heteroaromatic groups; Y is selected from the groupconsisting of C and N; and each of G₁-G₅ is selected from the groupconsisting of R and an electron withdrawing moiety, provided that when Yis N, G₁ is not present in the structure and at least one of G₁-G₅ is anelectron withdrawing moiety.
 9. The photoresist composition of claim 8wherein at least one of G₁-G₅ is an electron withdrawing moiety selectedfrom the group consisting of CN, NO, NO₂, Cl, Br, I, SO₂Me, and CHO. 10.The photoresist composition of claim 9 wherein at least one of G₁-G₅ isselected from the group consisting of CN and NO₂.
 11. The photoresistcomposition of claim 9 wherein at least two of G₁-G₅ are electronwithdrawing moieties.
 12. The photoresist composition of claim 8 whereinsaid onium cationic component is selected from the group consisting ofsulfonium cations and iodonium cations.
 13. The photoresist compositionof claim 12 wherein said onium cationic component comprises an aromaticmoiety.
 14. The photoresist composition of claim 13 wherein said oniumcationic component has a structure selected from the group consisting of

wherein each of R₁, R₂, R₃, R₄, and R₅ is independently selected fromthe group consisting of H; linear, branched, tertiary, or cyclic alkyl;linear, branched, tertiary or cyclic alkoxyl; unsubstituted andsubstituted aromatic groups; and unsubstituted and substitutedheteroaromatic groups.
 15. The photoresist composition of claim 8wherein said imaging polymer comprises a lactone moiety.
 16. Thephotoresist composition of claim 8 wherein said imaging polymer has aweight concentration ranging from about 5% to about 20% of the totalweight of said photoresist composition.
 17. The photoresist compositionof claim 8 wherein said fluorine-free photoacid generator has a weightconcentration ranging from about 0.5% to about 15% based on the totalweight of said imaging polymer.
 18. A method of forming a patternedmaterial feature on a substrate, said method comprising: (a) providing amaterial layer on a substrate; (b) forming a photoresist layer over saidmaterial layer, said photoresist comprising: (i) an acid sensitiveimaging polymer; and (ii) a fluorine-free photoacid generator comprisingan onium cationic component and an anionic component one of thefollowing two structures:

wherein: X is selected from the group consisting of S, O and NR; R isselected from the group consisting of H; linear, branched, tertiary, orcyclic alkyl; linear, branched, tertiary or cyclic alkoxyl;unsubstituted and substituted aromatic groups; and unsubstituted andsubstituted heteroaromatic groups; Y is selected from the groupconsisting of C and N; and each of G₁-G₅ is selected from the groupconsisting of R and an electron withdrawing moiety, provided that when Yis N, G₁ is not present in the structure and at least one of G₁-G₅ is anelectron withdrawing moiety; (c) patternwise exposing said photoresistlayer to radiation, thereby creating a pattern of radiation-exposedregions in said photoresist layer; (d) selectively removing portions ofsaid photoresist layer to expose portions of said material layer; and(e) etching or ion implanting said exposed portions of said materiallayer, thereby forming said patterned material feature.
 19. The methodof claim 18 wherein said radiation is provided by an ArF laser.
 20. Themethod of claim 18 wherein at least one of the G₁-G₃ moieties is anelectron withdrawing moiety selected from the group consisting of CN,NO, NO₂, Cl, Br, I, SO₂Me, and CHO.
 21. The method of claim 20 whereinat least one of G₁-G₅ is selected from the group consisting of CN andNO₂.
 22. The method of claim 20 wherein at least two of G₁-G₅ areelectron withdrawing moieties.
 23. The method of claim 18 wherein saidonium cationic component is selected from the group consisting ofsulfonium cations and iodonium cations.
 24. The method of claim 23wherein said onium cationic component comprises an aromatic moiety. 25.The method of claim 24 wherein said onium cationic component has astructure selected from the group consisting of

wherein each of R₁, R₂, R₃, R₄, and R₅ is independently selected fromthe group consisting of H; linear, branched, tertiary, or cyclic alkyl;linear, branched, tertiary or cyclic alkoxyl; unsubstituted andsubstituted aromatic groups; and unsubstituted and substitutedheteroaromatic groups.
 26. The method of claim 18 wherein said imagingpolymer comprises a lactone moiety.
 27. The method of claim 18 whereinsaid imaging polymer has a weight concentration ranging from about 5% toabout 20% of the total weight of said photoresist composition.
 28. Themethod of claim 18 wherein said fluorine-free photoacid generator has aweight concentration ranging from about 0.5% to about 10% based on thetotal weight of said imaging polymer.